1. Field of the Invention
This invention relates to the field of audible alarms in general, and in particular, to the field of residential smoke detectors, and the like.
2. Prior Art
Among audible alarm systems, the most popular in use today are audible alarm smoke detectors intended for residential use. Such smoke detectors are relatively small, are easy to mount or attach to walls or ceilings and are self-contained. Normally, a small nine (9 v) volt battery is sufficient to power such a detector for at least one year. Means are provided for sounding a soft alarm when battery power falls below safe operational levels. Such detectors typically operate on ionization chamber or photoelectric principles, and some on both. Such smoke detectors are widely sold under a variety of popular trademarks, and are relatively inexpensive. One such detector which has both ionization chamber and photoelectric detectors is described in U.S. Pat. No. 4,225,860-Conforti. The advantage of using both kinds of detectors is that ionization chamber detectors tend to be more sensitive to generally invisible constituents of products of combustion, whereas photoelectric detectors tend to be more sensitive to visible products of combustion. Photoelectric detectors are also more susceptible to generating false alarms, for example on the basis of atmospheric dust or smoke from a cigarette.
In view of the reasonable expense in purchasing one or more smoke detectors, and in view of their sophisticated operation, smoke detectors have become popular and widely accepted. Notwithstanding the justified reliance which the public has demonstrated on such smoke detectors, they suffer from an inherent operational defect.
If, for example, a smoke detector is installed in a basement, and an occupant is in a second or third floor bedroom, either sleeping or listening to loud music, for example, there is a chance that such a person will not hear the alarm being sounded. Even if a number of smoke detectors are disposed at various locations throughout the building, it is apt to take quite some while for detectable products of combustion to reach a smoke detector within ear-shot, or audible range, of that person in order to sound an effective warning. By the time the nearest smoke detector detects a fire, escape routes may already be blocked by the fire.
Heretofore, two approaches have been utilized to deal with this problem. One approach involves an alarm network, having a plurality of alarms, each of which is wire connected to a central control location. Such systems are disclosed in U.S. Pat. Nos.: 3,733,596-Arima; 4,141,007-Kavasilios, et al.; 4,161,727-Thilo, et al.; 4,162,489-Thilo, et al.; 4,176,346-Johnson, et al.; and 4,223,303-Albinger, Jr.. As may be appreciated, such systems require professional installation, as the wiring network must be routed through the entire building. Further, there is a danger that the fire itself will destroy the wire network. Unless such a system can be built integrally with a structure, it is unlikely to be as successful in the marketplace as the self-contained units. Although such systems provide higher levels of safety, they are not considered by most people to be "too inexpensive not to purchase". Such feelings with respect to cost and safety may be the foremost reason that existing smoke detectors are as widely used today as they are.
Accordingly, it has been necessary to devise a system whereby self-contained smoke alarms can be easily interconnected without actually being wired together. One method employed in interconnecting alarms in general, principally with a central location, is the use of radio transmission or ultrasonic sound transmission. Burglar and fire alarm systems according to this approach are described in U.S. Pat. Nos.: 3,192,516-Simpkins, et al.; 3,973,250-Uffelman; 4,001,805-Golbe; 4,160,246-Martin, et al.; 4,189,720-Lott; and 4,191,947-Bouchard, et al., and Japanese Pat. No. 52-51896. Light pulse systems are described in U.S. Pat. Nos.: 3,683,352-West, et al.; 3,714,647-Litman and 3,805,257-Litman, et al.. These approaches require additional sophisticated and expensive circuitry, are subject to interference from adjacent systems, much like automatic garage door openers, and represent a segnificant additional power drain on the battery system. Such an approach is clearly not feasible with self-contained units. Further, neither radio waves, ultrasonic whistles nor brief flashes of light will serve to enhance the alarm capacity (ability to make sounds which attract attention) of an audible alarm unit.
This invention overcomes all of the problems noted above, by utilizing the existing audible alarm signal as the means by which otherwise self-contained smoke alarms can communicate with one another without being wire connected to one another. Every alarm is designed to trigger an alarm signal in response to detecting an abnormal or adverse condition. In the case of smoke alarms, the abnormal condition is the presence of products of combustion in excess of predetermined safety limits. In the case of burglar alarms, a broken window or noise or unauthorized opening might be the abnormal condition sensed. This invention provides an auxiliary triggering mechanism for self-contained audible alarms. A preferred auxiliary triggering mechanism includes a sound detector, such as a transducer or microphone, a sound discriminator, which can identify the presence of an audible alarm of any similar detector by sensing certain characteristics of the sound, and means for enabling the existing audible alarm in the self-contained unit. Various arrangements of ever increasing sophistication can be utilized in the sound receiving and discriminating circuit. Such a circuit may be entirely electrical, or electro-mechanical in nature. If such an auxiliary triggering mechanism were incorporated into a number of self-contained smoke detectors disposed at various locations throughout a home or building, and a fire were to start at that location in the building most remote from a person occupying that building, within a short period of time after activation of the smoke detector closest to the fire, the smoke detector closest to the person would be activated, not necessarily by detection of the fire itself, but by detection of the audible alarm or alarms of the other detectors in the building. A further advantage of this system is that unlike radio, light, and ultrasonic sound based systems, a system according to this invention magnifies and multiplies the very sounds which alert persons to the need to run for safety. People have no means by which to detect radio waves or ultrasonic sounds and flashes of light are not acceptable warning signals, being most often dismissed as spurious and fleeting reflections of unknown origin.
This invention not only provides a reliable means for interconnecting self-contained audible alarms, which will enable all of the alarms in a system to be sequentially activated within a short time, but does so in a manner which utilizes existing components in each self-contained audible alarm, does so in a manner which provides minimum additional drain of limited battery power, and finally, does so in a manner which significantly multiplies that audible warning signal which can be perceived most easily by people. Such a device, incorporated into new audible alarm units, and added onto existing audible alarm units can save lives which are now being lost.